Origin and evolution of waters in the Hancheng coal seams,the Ordos Basin,as revealed from water chemistry and isotope(H,O,^(129)I) analyses  

作　　者：MA XingZhi SONG Yan LIU ShaoBo JIANG Lin HONG Feng 

机构地区：[1]Research Institute of Petroleum Exploration and Development,PetroChina [2]Key Laboratory of Basin Structure and Petroleum Accumulation,China National Petroleum Corporation [3]State Key Laboratory of Enhanced Oil Recovery

出　　处：《Science China Earth Sciences》2013年第11期1962-1970,共9页中国科学（地球科学英文版）

基　　金：supported by National Basic Research Program of China(Grant No.2009CB219601)

摘　　要：The coal seams in the Permian Taiyuan Formation and the Carboniferous Shanxi Formation are the primary reservoirs for the coalbed methane （CBM） in the Hancheng region in the Ordos Basin. In this paper, the origin and evolution of waters associated with CBM production were studied on the basis of water chemistry and isotopes including the chloride and iodine compositions, oxygen and hydrogen stable isotopes, and radioactive isotope ratio of ^129I/^127I. The ratio of ^129I/^127I of water was determined by accelerator mass spectrometry （AMS）. The result shows that the formation water is of NaHCO3 and NaCl types with the total dissolved solids （TDS） varying from 1532.29 mg/L to 7061.12 mg/L. The values of ^129I and I/CI ratio indicate that the formation waters were diluted by meteoric water. The ^129I/^127I ratios range from 6.6×10^-13 to 1459.5~10-13. The ^129I/^127I ratios for most of the samples are between the ^129I/^127I initial value and that of recent anthropogenic water. This age of the formation water samples, obtained through the ^129I decay curve method, ranges from 0 Ma to 18.5 Ma, suggesting that the waters from the Taiyuan Formation and the Shanxi Formation are very young. Two different origins of water are identified in the Hancheng region. One group is dominated by pre-anthropogenic meteoric water, and is characterized by ^129I/^127I ratios lower than the initial value of 15×10^-13 and δD, δ^18O values of waters below the Global Meteoric Water Line. The other group is characterized by ^129I/^127I ratios in excess of 15×10^-13, which has undergone variable degrees of dilution by recent anthropogenic water.The coal seams in the Permian Taiyuan Formation and the Carboniferous Shanxi Formation are the primary reservoirs for the coalbed methane(CBM)in the Hancheng region in the Ordos Basin.In this paper,the origin and evolution of waters associated with CBM production were studied on the basis of water chemistry and isotopes including the chloride and iodine compositions,oxygen and hydrogen stable isotopes,and radioactive isotope ratio of129I/127I.The ratio of129I/127I of water was determined by accelerator mass spectrometry(AMS).The result shows that the formation water is of NaHCO3and NaCl types with the total dissolved solids(TDS)varying from 1532.29 mg/L to 7061.12 mg/L.The values of129I and I/Cl ratio indicate that the formation waters were diluted by meteoric water.The129I/127I ratios range from 6.6×10 13to 1459.5×10 13.The129I/127I ratios for most of the samples are between the129I/127I initial value and that of recent anthropogenic water.This age of the formation water samples,obtained through the129I decay curve method,ranges from 0 Ma to 18.5 Ma,suggesting that the waters from the Taiyuan Formation and the Shanxi Formation are very young.Two different origins of water are identified in the Hancheng region.One group is dominated by pre-anthropogenic meteoric water,and is characterized by129I/127I ratios lower than the initial value of 15×10 13andδD,δ18O values of waters below the Global Meteoric Water Line.The other group is characterized by129I/127I ratios in excess of 15×10 13,which has undergone variable degrees of dilution by recent anthropogenic water.

关 键 词：water associated with CBM HALIDE stable isotopes ^129I/^127I DATING evolution 

分 类 号：P618.13[天文地球—矿床学] P597[天文地球—地质学]